Added clamping to textstorage.attributedSubstring to avoid out-of-bounds crashes (#305)

Author: rajdeep

Proton/Sources/ObjC/PRTextStorage.m

@@ -73,6 +73,17 @@ - (void)edited:(NSTextStorageEditActions)editedMask range:(NSRange)editedRange c
     [self.textStorageDelegate textStorage:self edited:editedMask in:editedRange changeInLength:delta];
 }
 
+- (NSAttributedString *)attributedSubstringFromRange:(NSRange)range {
+    NSRange rangeToUse =[self clampedWithUpperBound:self.length location:range.location length:range.length];
+    return [super attributedSubstringFromRange: rangeToUse];
+}
+
+- (NSRange)clampedWithUpperBound:(NSInteger)upperBound location:(NSInteger)location length:(NSInteger)length {
+    NSInteger clampedLocation = MAX(MIN(location, upperBound), 0);
+    NSInteger clampedLength = MAX(MIN(length, upperBound - clampedLocation), 0);
+    return NSMakeRange(clampedLocation, clampedLength);
+}
+
 - (void)replaceCharactersInRange:(NSRange)range withAttributedString:(NSAttributedString *)attrString {
     // TODO: Add undo behaviour
 

Proton/Tests/Core/TextStorageTests.swift

@@ -131,4 +131,13 @@ class TextStorageTests: XCTestCase {
         XCTAssertEqual(attrs[NSAttributedString.Key("attr2")] as? Int, 2)
         XCTAssertEqual(attrs[NSAttributedString.Key("attr3")] as? Int, 3)
     }
+
+    func testReturnsSubstringWithClampedRange() {
+        let textStorage = PRTextStorage()
+        let testString = NSAttributedString(string: "test string")
+        textStorage.replaceCharacters(in: .zero, with: testString)
+
+        let substring = textStorage.attributedSubstring(from: NSRange(location: 5, length: 50))
+        XCTAssertEqual(substring.string, "string")
+    }
 }